Shelf Watch Late July'15 and Superstock Randoms

The reddits have been doing a great job of watching the various stores and vendors lately, so just a few local sightings:

Buzzbee Tyrant at Wal-Mart Lakeland, FL

The larger model of Buzzbee's breakout magfed 20mm products, this thing is huge, and retails for about $20 and comes with a 12 round magazine. You can check out the reviews and internals on reddit.

The lack of a stock and pump grip are inexplicable, and my only real issue with Buzzbee's design decisions. This particular gun is close to being a market segment dominator. If it were to have a stock and a pump grip, it would easily throw all of Nerf's current and likely future (since they closed the door on magfed, idiots they are) Mega offerings into the junk pile of obsolescence.

If you ask me, the smaller version (Boss) should have remained a purpose-made pistol with a top slide, and this, instead of being simply the same functional thing with extra empty space, should have had a stock, and a pump grip.

Oh, if you haven't heard, this gear - mags, guns, ammo - are all compatible with Nerf stuff and other aftermarket products intended to be compatible with Nerf. The industry standards are forged. Bring on the competition.

And now we have Crossbolts at a TRU, same city:

Nuff said, they are out there if you want them.

Now here's the story behind the last post. T3.1 flywheel cage. Nice buildup, and those Rayven flywheels did shoot real nice...

...but the shaft fit troubles continue. You can see that bottom fly has backed off the shaft.

And left a nice witness mark in the cage.

Consider that a failed experiment. Rayven flywheels are NOT suitable for 180 service. The torque is probably to blame, every hard start makes the fly creep a bit on the shaft until it loses too much engagement and the imbalance starts levering it around until it comes off.

I might try coatings on the shafts to tighten the fits. You can't bond to Delrin so anaerobic assembly compounds (Loctite and bearing lockers) are off the board but the shaft could be pre-coated with something to tighten the press fit. CA glue, likely candidate.

Shaft fit problems are one of the biggest headaches with flywheel guns. I have seen what should be solid setups spin flies off with no rhyme or reason. It's half the reason I carry a secondary. I have high hopes for the current T3.1 setup, it is the same as the T2.1 that has been going without any movement of the flies since day one well over a year ago.

While I had it apart, this is the modular cage unplugged. 14AWG Teflon main leads and 16 jumpers, genuine Deans. This is a place where Deans is the only real choice because...

...this is where the connector pair goes when installed. OldNoob, this might give you ideas for how to not have any under-cage space in a build and keep cage modularity. Wire straddles the screw bosses.

Now, after this happened, I quickly snagged some Rapid Reds in trade for stuff, and popped a fly set in. I was planning on going to UGA '15 and I would have run these for that, but people flaked and it didn't happen.

Rapid Red flywheels are decent. Good tight shaft fits, good quality and balance, similar rim thickness and inertia to Stryfe flies. They can work, and work reliably, but I noticed a bothersome issue with them.

They have a real hard time developing the normal buildup layer. This was after cleaning with IPA and then 400+ rounds of breakin! There was a lot of dart material in the receiver and handguards near the cage and not that much on the flywheels.

Cause is definitely the surface finish on these. It is a fine blast or pebble type texture, like you would find on some ABS parts as a finished exterior surface.

Apparently the mirror polish on older type flywheels is critical to the buildup development. A bit counterintuitive but definitely an important bit of flywheel engineering.

Without buildup established more than ~20% on these, they were missing 5-10 fps versus Stryfe/Rayven flies.

Stryfe (shiny) on left, Rapidred (dull) on right. Note it appears they shot blasted the entire mold for these things for reason unknown, and it is clearly a different tool based on the position of gate marks.

I find this quite strange about Hasbro. They will manufacture 2, 5, 10... guns that share functionally identical parts, but it's almost like the designers operate in total isolation. Sometimes there are parts that are functionally identcial, but not mechanically identical and not interchangeable. Other times, as with the whole streamline flywheel lineup, parts will be mechanically more or less identical, and interchangeable, but are different, each designed from scratch and manufactured differently. Such is the case here.

Why do all these guns have their own unique flywheels made on unique tooling? How can this possibly be efficient or cost effective?

In any case Stryfe flies went in and breakin shoot commenced as usual. Buildup is returning and is about 75% and it is back on the ready line. Left the 1600mAh battery in there for now because it's big enough, I will probably put the 2500mAh in something new to test.

The WASP was also fielded a couple days back, along with its Blastersmiths UK Mk4 holster:

This combo did extremely well. Had zero issues with comfort or rotation.

I also switched my dump pouch to its final location, and played my first game ever without sending a single magazine to the deck. Things are finally, 5 years later, starting to fall into place with gear. For the sort of player I am, I never have been on the bleeding edge in that regard.

PSA: Rayven Flywheels = No Go

I just played a game on a backup gun. Hooray for backup guns! Lesson here, don't run Rayven flywheels no matter if the shaft fits seem tight or not! They WILL walk off the shaft sooner or later.

I was also seeing a very noticeable disparity in response between Rayven flywheels and Stryfe flywheels. The latter are lighter. Inertia may seem like your friend, but it is your enemy.

Off to hunt a good balanced set of Stryfe flywheels once again.

The upside is that it gives me an excuse to stick that shiny new 2500mAh battery in there and nix the JST-XH while I am at it.

Monolith Developments

If you follow my nerf stuff you will know I build these cylindrical high current lithium-ion packs. Here are the latest experiments.

First of all I am giving this Samsung INR18650-25R cell a shot.

Just a clarification on what I talked about earlier:

The Samsung 20R and 25R are not quite "the same cell with increased capacity". The 25R sags slightly more under heavy continuous loads. The cell that compares on IR and 20-30A performance to the Sonys I have used in the past is the 2000mAh 20R. This one trades off punch for capacity to some extent.

There is a 2500mAh cell that doesn't trade off anything, and that is the Sony VTC5, which is extremely expensive as cells go but is what I would use if someone wanted the best 18650 cylindrical pack available.

I went with the 25 this time because I want to test it. If it can perform great on a RS build and have 2500mAh at this cell cost, it has an application. And it certainly should perform great. This is all hair splitting and this cell still has major guts.

This is what the welded blank looks like for a Tacmod type, 2 cell stick. As usual - double thickness with 8x0.15mm nickel tab stock, split ends, 8 welds per tab end with the redneck 1 farad cap/SCR spot welder.

I want to upgrade that welder with another capacitor so I can increase the electrode tip size and make a bigger weld. However it does fine and I have never had a weld problem or a tab ever come off a cell. I even accidentally shot through 2 layers of tab at once during this build and it welded them to the cell just fine.

This is what it looks like wired. 14AWG discharge leads and 20AWG balance taps, silicone insulated fine strand.

Above pack shrinkwrapped and terminated.

As usual in end-to-end packs there is an insulating mica board piece under that center tab on the positive side.

This is something new I am trying; W.S. Deans micro connectors as balance taps.

Typically I have used industry standard JST-XH connectors for balance taps and I buy prewired pigtails. I have tried as hard as I could to be standard, but I have had too many problems with JST-XH. In my opinion it is just not durable enough to be used repeatedly and constantly for charging.


It is also difficult to terminate in the field. It is a common type of production connector with separate contacts designed to be crimped to the wire and then inserted into the plastic housing. The pigtails (buying and working with) are a bit of a pain and I don't like the quality of the wire I get with them.


In general I don't like connectors in which the pin is removable. I have had these JSTs spit out pins when plugged in. This is obviously bad, as you could have live metal floating around inside a gun.
 
2 cell packs have 3 wire tap cables. 3 cell packs have 4. 1S packs don't have or need balance taps. Those are the majority of nerf applications and this type connector covers them. The 4 pin Deans micro is usually red and the 3 pin always black, a convenient color code.

At least for internal charge systems, I will be switching my batteries to this style connector.

Size comparison. The Deans 3 pin is actually smaller and more streamlined than the JST.

The mating connector. These are polarized of course. One pin is offset. I wire the offset pin to the positive end of the pack.

Isn't that neat?

Mega and micro comparison to this pack.

That ought to give an idea of where these can be fit. Primarily these sticks are a stock or buffer tube battery.

With a bunch of other assorted packs. Red cells are Sanyo UR18650SAX, green cells are Sony US18650VTC3, black pack is a 4S Sanyo SAX for a Stampede.

Tech: The Resistive-Center Rapidstrike Control Circuit

This is an idea for a modification of the live-center RS control scheme, which was inspired by this post. Let's start by taking another look at the diagram showing various possible diode locations in a live-center RS control circuit.

In particular, I'd like to draw your attention to the diode location on the green wire. This was previously identified as an erroneous diode location, as placing a diode here would only slow automatic operation of the pusher and not drop ROF, with the implication that there is no benefit to having a diode in this location.

This is only mostly right: there is a benefit to having a diode here, albeit a small one. This diode would provide a small stability benefit, by turning what would otherwise be a runaway into a single or a small number of trailing shot(s). Planned use of such a system would be a prime example of smart-dumb engineering: smart because it solves a problem, and dumb because a well-made system damn well should not have this problem in the first place. A voltage drop in this location is suitable as a protective measure in a fully stable build which is at risk of becoming unstable. There are several ways that this could happen - degradation of parts resulting in an increased braking resistance was previously noted. The use of batteries with an unexpectedly high voltage is also a possibility. Notably, NiMH batteries may have a higher than expected voltage when hot off of the charger, depending on the charger.

Now: what if we used a resistor?

Using a resistor in place of a diode when dropping ROF is usually not a great idea. A resistor which produces a similar drop in ROF to a given set of diodes will produce a greater increase in lock time, which is undesirable. Furthermore, it is usually pretty easy to tell in advance how much of a voltage drop you want when using diodes: regardless of what motor you have, a voltage drop produced via a diode will have the same effect as if you had used a battery of a lower voltage, whereas with a resistor, the relationship between the ROF and the resistance is more complex and depends on the battery voltage and the motor used.

However, dropping ROF is not what we want to do here, and here, resistors can do something very useful which diodes cannot: they can provide protection in the event of a stalled pusher.

Let's do some back-of-the-envelope calculations to see what sort of resistance we would need here. Let's assume a freshly charged 3S LiPo pack, as this voltage (12.6 V) is the highest that we are likely to see, and an FK3240 on the pusher, because this is a fairly common pusher motor with known specs. An FK3240 draws 1.54 A when operating at maximum efficiency at 3 V, and the effects of a stationary rather than moving commutator on motor burnout are difficult to estimate, so 1.5 A serves as a conservative-ish rough estimate of how much current an FK3240 can comfortably withstand while stalled.

This suggests that the highest resistance which we might want is 8 Ohms. Realistically, we could probably get away with something lower.

What effect will this have on the speed of the automatic operation of the pusher rod? Most of the time, this will not be a concern due to the momentum of a RS's pusher box. The fact that a dead-center RS will terminate a good proportion of the time with the pusher rod nearly fully retracted should give an indication of how significant this momentum is. The worst case would be a marginal trailing shot - i.e. a shot where the pusher is left on the far side of the braking region with little momentum, and the automatic operation of the pusher rod carries the rod through an entire cycle. As the pusher motor experiences a load which is not known and which varies over the stroke, the effect of this resistance is difficult to calculate. However, it is worth noting that 8 Ohms is pretty close to what some people who use resistors to drop ROF use - see this post where Boff of the BirtNerf forums links to some 7.5 Ohm power resistors which he used in a batch of RSs.

So, there you have it: the resistive-center control circuit. Start with a live-center circuit, and put an appropriately-rated resistor on the wire that runs between the battery and the cycle control switch.

Advantages:

• Predictable trigger response, as a standard live-center control circuit.
• Reliable pusher position control, as a standard live-center control circuit.
• Protection in the event of a pusher crash and any other sort of pusher jam. This protection is inherent to the circuit, and does not rely on the user to release the trigger quickly. 

Disadvantages

• Trailing shots are possible, and may be fired with a greater delay than with a standard live-center circuit. 
• Safety, though less so than with a standard live-center circuit. An unattended powered blaster which suffers a mechanical failure in the cycle control switch may have its pusher operate continuously. An appropriately rated resistor should reduce the fire hazard, prevent damage to the motor, and prevent battery damage through excessive discharge rate. Battery damage through overdischarge will take considerably longer than with a standard live-center circuit. 

This control circuit is as of now untested, so caution dictates that I not recommend it too enthusiastically. With that being said, this circuit should serve as a good compromise between a live and a dead center.

The Situation With "Meishel" Motors

When I did my electric pistol build, I decided on these 4666kv generic FK130 motors that redditor /u/Meishel found on ebay a while back. However, what arrived in the mail was not in fact the same motor.

It turns out there has been a substitution across multiple sellers, perhaps at the supplier level, of a vaguely similar motor and I was one of the first to receive the new ones. At the time, I was oblivious to the difference, because I hadn't used the original Meishel motor. It wasn't until I put the thing together that I noticed anything remotely amiss (the high speed and noise of these things compared to what I was expecting them to do), and then after redditing my blog post, Meishel commented. Further research blew the can of worms wide open. So here's the deal.

This is a true "Meishel" FK130 motor. Note the SQUARE vent hole in the can, the standard zincplate finish on the can, and the standard length FK-series shaft end which is exactly like the one on the Mabuchi FK180SH-3240 and other Mabuchi FK motors you may have seen.

Proper specs for torque and current draw are maddeningly nonexistent on these, but what we know is "28000rpm @ 6.0V" which gives a kv of 4666.

These motors are well tested with 2S lipo batteries. They turn at ~34500rpm unloaded giving nominal performance, and have response and torque noticeably inferior to the Falcon WFK130SZ-2190, but pretty damn good for a 130 motor, especially for one that uses a simpler and more space efficient 2 cell battery and is thus well suited to pistols where fitting in a 3S pack with enough guts for Falcons would be difficult.

Now this motor is the new one people are getting from former Meishel listings which is NOT a Meishel motor. Note rectangular vent hole, longer shaft (only a good feature for flywheels) and can that appears hot galvanized or plated with heavier zinc.

(right)

This motor is rated at 25000rpm @ 4.8V, giving a kv of 5208. It is wound substantially hotter than a "Meishel".

On 2S lipo, this motor turns at circa 38000 rpm. This is not an optimal setup, speeds over ~35K are not helping with velocity and might decrease accuracy and consistency. Plus the obvious noise. Durability and reliability are not well known for this combo but I don't expect trouble out of these from how mine have acted so far.

Some comments about reliability concerns, brush gear, LiFePO4 batteries, and such for this 5200kv FK130 "banshee" motor in this reddit thread.

Real funny, Coop.

The thumbnail from Cooper and Unicorn Tactical's new "tactical" parody video. I won't be linking it from here, but check it out, it's worth a watch, it's got rolling around in a pile of darts and everything. But what's with that gun? Let's have a closer look:

I see what you did there.

PS: Countersink your damn screws.

WASP Completion

WASP = WASP Automatic Superstock Pistol

This was where I left it:

Now the new bodywork:

And paint. Trivia: Everything red of mine has been sprayed with the same single can. "DZ Customs Red" is ACE Hardware "Rust Stop" (Rustoleum knockoff) "Regal Red" enamel. That can is about 10 years old and has sprayed a bunch of mower parts and other random things too, and now 4 guns! And there is still paint left in it!

One of the great things about the Rustoleum industrial finish, it covers forever and beyond. Super cheap and handy. I spray the white stripes over the red in one coat, too. Perfect coverage, though I could get smoother paintjobs if I would be more careful and patient and buy some fresh paint.

That was a while back. The battery and motors arrived recently and I put this thing together.

Generic FK130SH 4666kv "Meishel" 5200kv "Banshee" (This is NOT a "Meishel" motor! I have a post upcoming about this situation) on right, Mabuchi FK180SH-3240 for comparison on left. As you can see these things have vented cans in just the right place for Nerf cages, and a slightly longer shaft, both good features.

Installed in a Stryfe cage.

The battery I am using, a Zippy Compact 2S 850mAh 25C.

The only battery box mod, aside from gutting out all the AA related stuff from the inside, is to grind this spot. This is where the wires exit the wrapping of the pack and the relief avoids pinching them.

Dropped in place.

Installed. There is a PVC piece added to prevent the pack from moving forward, and I have replaced the JST RCY with a Deans Ultra.

Everything crams in nicely. The battery box cover has had the ribs removed on the backside

Closed.

Internals. Wired with 16AWG teflon, full size micro, all standard stuff. You can also see the "vortex" muzzle device here

This feed guide is one of the defining features that separates this from "just a Stryfe". It is ~2mm sheet, and bonded to the underside of the old support area for the lockbolt/dart sensor that of course went in the trash.

And this is what it does; support the top round in the mag and prevent it from working upward through the feed lips over time. This is going to be a sidearm, so this is a very necessary feature for reliability. It prevents malfunction clearance without dropping the mag and prevents toploading, but it allows trouble-free use of mags with very strong springs (like 6-rounders, which are what will be used in a pistol) over any period of time.

You can also see the spring feed guides installed in the cage. These are there to provide spring pressure to hold darts in the mag and avoid any remote chance of the dart working forward into the flywheels and locking them up.

With my primary.

Now I just have to wait for that holster to arrive.

I am happy with the results of this build (which are alright response and nominal velocities), but I don't like how loud and rough it is. It could use a set of better balanced flywheels (but definitely can't handle any more flywheel mass). These motors rev a bit too high in my opinion, and the battery is also too small and has too high an IR to get either optimal motor performance or optimal service life out of the battery. I still don't like flatpak lipo and I still don't like 130 motors.

However, in terms of a cheap power system ($5.10 battery, $3.58 motor set) that is available at present and fits into a pistol form factor, it is pretty damn good. It has a mean buzz and a nasty sting and it will sure get me out of more bad situations than a single-action revolver.